But of course it has to do with blocksize.
Blocksize is a check on economies of scale so as to level the playing ground. It is absolutely necessary while Bitcoin is still relatively small. Without it the entities with the most resources will make use of the technology available to run out of the market any smaller players.
that is only true if the entity with the most resources has more than 51%.
otherwise i expect smaller players to team up in such cases and ignore blocks as soon as a big player start to behave badly.
it is in their best interest to do that.
we can see this with: most home miners go to the biggest pool like flies going to the brightest light. but - until now - whenever a pool got to much hashing power the community realized that it is bad and hashing power got more distributed again.
edit: imho:
in the long run bitcoin can only stay decentralized when many households have a miner at home. eg an electric heating device